The invention is based on a priority application EP04291696.5 which is hereby incorporated by reference.
The present invention concerns the field of the telecommunications, more particularly in relation to services available through mobile terminals connectable to communication networks.
The present invention concerns more specifically a method and a network allowing to provide multicast data transmission, and associated services, to a user with a mobile terminal, in particular with reduced needs in network resources.
In a discontinuous coverage network (also known as “info-station” system), downstream or downlink data flows (necessary to provide certain services at a mobile terminal) are managed and handled by taking into account the specific nature of the connection.
Thus, when a mobile terminal arrives in a hotspot (area where the radio coverage is available), it retrieves a large amount of data which is necessary for providing the user with the service until said mobile terminal arrives in a new hotspot.
A significant part of the traffic that such a network will support will be of the multicast type. For instance the traffic related to a diffusion of a “multimedia newspaper” everyday towards a group of people who have subscribed for this service, can be considered as a multicast service.
In a network where the final user has continuous connectivity, the multicast nature of the traffic allows to save transmission resources and to reduce the work load of the server by using adequate routing techniques as depicted in the FIGS. 1A and 1B of the drawings.
In a discontinuous coverage network, only a few percentage of the users belonging to a given multicast group are connected (i.e. present in a hotspot or within a coverage area) at the same time.
This discontinuity of the communication link and the resulting random connections of the users of a multicast group, decreases significantly the multicast gain mentioned before.
FIG. 2 of the drawings illustrates this loss of resources' gain in case of two clients or users connected at different times to a data server providing multicast data and services, as it is usual in discontinuous coverage networks.
One understands that, as the two clients are not connected at the same time, the transmission of multicast data consumes almost as much resources (in particular server resources) as the transmission of normal (not multicast) data.
Indeed, despite the multicast nature of the data, the transmission to the clients or users of a concerned multicast group is performed by the server by using as many point to point connections as there are clients.